PPL(A) 040 Human PerformanceRevision notes and practice questions

PPL 040 Human PerformanceFree sample, 10 questions

1. 1Studies of aviation accidents show that human factors play a part in roughly what proportion of them?

   1. About 20 to 30 %.
   2. About 40 to 50 %.
   3. About 70 to 80 %.
   4. About 95 to 100 %.
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   Answer C. Around 70 to 80 % of aviation accidents involve a human factors component. As engines and airframes became more reliable, technical causes fell and the human share became dominant. This does not mean the pilot alone is to blame: maintenance, air traffic control and the organisation are humans too.

2. 2A pilot climbs from sea level to 18 000 ft, where the atmospheric pressure is about half its sea level value. Which statement about the oxygen in the air is correct?

   1. Oxygen makes up only about 10 % of the air, so its partial pressure is about halved.
   2. Oxygen still makes up about 21 % of the air, but its partial pressure is about halved.
   3. Oxygen still makes up about 21 % of the air, and its partial pressure is unchanged.
   4. Oxygen makes up only about 10 % of the air, but its partial pressure is unchanged.
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   Answer B. Dry air contains about 78 % nitrogen, 21 % oxygen and 1 % other gases, and this proportion stays the same at every altitude. By Dalton's law, the partial pressure of oxygen is the total pressure multiplied by 0.21, so it falls with the total pressure. At 18 000 ft the pressure is halved, so each breath delivers about half the oxygen pressure available at sea level.

3. 3Which statement about vision at night is correct?

   1. The cones, mainly at the periphery of the retina, need about 30 minutes to adapt fully to darkness.
   2. The rods, mainly at the periphery of the retina, need about 30 minutes to adapt fully to darkness.
   3. The rods, concentrated in the fovea, need about 7 minutes to adapt fully to darkness.
   4. The cones, concentrated in the fovea, give the sharpest night vision, so a faint light is best seen directly.
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   Answer B. Rods lie mainly at the periphery of the retina, work in low light and do not perceive colour; they need about 30 minutes to adapt fully to darkness. Cones are concentrated in the fovea, give colour and detail in daylight and adapt in about 7 minutes, but they are ineffective at night. The centre of the visual field therefore becomes a night blind spot, so a faint light is best seen by looking 5 to 10° to one side of it. A single bright light can destroy dark adaptation.

4. 4A pilot has his last drink at 23:00, when his blood alcohol concentration is estimated at 1.6 g/L. Assume an elimination rate of 0.15 g/L per hour, a blood alcohol limit of 0.2 g/L and a minimum of 8 hours between the last drink and flight. What is the earliest time at which both conditions are met?

   1. 06:20
   2. 07:00
   3. 08:20
   4. 09:40
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   Answer C. The concentration must fall by 1.6 - 0.2 = 1.4 g/L, which takes 1.4 / 0.15 = 9.33 h, that is 9 h 20 min, so the limit is reached at 08:20. The 8-hour rule alone would give 07:00, but the later of the two times governs. 06:20 uses a 0.5 g/L limit and 09:40 is the time to reach zero. Nothing speeds up elimination, and a hangover can still impair performance after the alcohol has gone.

5. 5In the simple model of human information processing, which sequence is correct?

   1. Stimulus, perception, sensory memory, action, decision.
   2. Stimulus, sensory memory, perception, decision, action.
   3. Perception, stimulus, decision, sensory memory, action.
   4. Stimulus, long-term memory, sensory memory, perception, action.
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   Answer B. A stimulus first reaches the sense organs and is held very briefly, less than a second, in sensory memory. Perception then gives it a meaning using knowledge stored in long-term memory, a decision is made in working memory and the action follows. Attention filters the whole chain and feedback lets the pilot see the result of his action. Perception cannot come before the stimulus, and sensory memory always comes first.

6. 6A pilot unsure of his position sees a lake and a town and decides they are his planned checkpoint. He then ignores a railway line that should not be there according to his map. Which bias is shown?

   1. Risky shift: as part of a group, he accepts a higher risk than he would accept alone.
   2. Anchoring on weather: he gives too much weight to the first forecast he received.
   3. Confirmation bias: he keeps the information that supports his idea and ignores what contradicts it.
   4. Hypovigilance: low workload during a long cruise has reduced his level of alertness.
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   Answer C. Once a mental model is formed, new information tends to be interpreted so as to confirm it, and contradicting clues are dismissed. This confirmation bias is a classic cause of getting lost: the pilot makes the ground fit the map instead of checking the map against the ground. The defence is to look actively for features that would prove the position wrong. The risky shift needs a group decision, which is not the case here.

7. 7How does a pilot's performance usually vary with the level of arousal or stress?

   1. It rises to an optimum at a moderate level, then falls as the level keeps increasing.
   2. It falls steadily from the lowest level upwards, so any level of stress is harmful.
   3. It rises steadily with the level, so the more stress there is, the better it becomes.
   4. It stays constant until the pilot panics, then drops suddenly to almost nothing.
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   Answer A. Performance follows an inverted U curve against arousal: too little leads to boredom and hypovigilance, a moderate level gives the best performance and too much leads to fixation, omissions and hasty decisions. Some stress is therefore useful because it keeps the pilot alert. The trap is to think that stress is always harmful. Underload degrades performance just as overload does.

8. 8During the pre-flight checks, a pilot misinterprets an ambiguous item in the aircraft checklist. In the SHELL model, which interface does this error belong to?

   1. Liveware-Software.
   2. Liveware-Hardware.
   3. Liveware-Environment.
   4. Liveware-Liveware.
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   Answer A. In the SHELL model the pilot (Liveware) sits at the centre and errors arise at the interfaces. Software covers procedures, checklists, manuals and charts, so a misread checklist is a Liveware-Software problem. A badly placed fuel selector would be Liveware-Hardware, turbulence or noise Liveware-Environment, and a misunderstanding with ATC or a passenger Liveware-Liveware.

9. 9A pilot at rest suddenly loses his oxygen supply. What is the approximate time of useful consciousness at 18 000 ft and at 25 000 ft?

   1. About 20 to 30 minutes at 18 000 ft and 3 to 5 minutes at 25 000 ft.
   2. About 3 to 5 minutes at 18 000 ft and 20 to 30 seconds at 25 000 ft.
   3. About 2 hours at 18 000 ft and 20 to 30 minutes at 25 000 ft.
   4. About 20 to 30 minutes at 18 000 ft and 9 to 12 seconds at 25 000 ft.
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   Answer A. The time of useful consciousness is the time during which a pilot can still act effectively, which is shorter than the time to unconsciousness. It is about 20 to 30 minutes at 18 000 ft and 3 to 5 minutes at 25 000 ft; 9 to 12 seconds applies only at 43 000 ft and above. Physical effort, stress, cold, smoking, alcohol and fatigue shorten it, which is why supplemental oxygen is needed from around 10 000 ft.

10. 10Which technique gives the best chance of detecting other traffic during a VFR flight?

    1. Move the eyes in short, regular steps of about 10°, pausing about 1 second on each sector.
    2. Sweep the eyes continuously and smoothly across the whole horizon without stopping.
    3. Stare at a fixed point ahead and rely on peripheral vision to detect any movement.
    4. Look mainly straight ahead, since traffic on a collision course always moves fast.
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    Answer A. The eye sees sharp detail only in a small central area and perception is suppressed while the eyes are moving, so a continuous sweep misses traffic. Scanning in steps of about 10°, pausing about 1 second on each, brings each part of the sky into central vision. An aircraft on a collision course keeps a constant relative bearing and appears motionless, growing only at the last moment. Over a featureless sky the eyes also relax to a focus of 1 to 2 m (empty field myopia), so refocus regularly on a distant object.